noun
Japanese freshwater crab
Refers specifically to Geothelphusa dehaani, a small crab found in mountain streams and rivers across Japan. Often kept as a pet or used in environmental education.
子供の頃、川でサワガニを捕まえた。
When I was a child, I caught freshwater crabs in the river.
サワガニはきれいな水にしか住めない。
Freshwater crabs can only live in clean water.
モクズガニ is a different freshwater crab species (Eriocheir japonica) known for its hairy claws and migratory behavior, while サワガニ is a fully freshwater species that completes its life cycle in streams.
Compound of 沢 (sawa, 'mountain stream') and 蟹 (kani, 'crab'), describing its habitat. The exact historical derivation is straightforward.